Temporal Shaping of the Pre-beam Formed RF data
The analog signal from the transducer is fed to a Voltage Controlled Amplifier (VCA) which performs: 1. termination 2. amplification 3. low pass filtering. All three functionalities of the VCA can be digitally programmed. The VCA Amplification determines the gain of the amplifier. The VCA LPF sets the cutoff frequency of the low-pass filter on the VCA. VCA LNA Input Clamp determines the LNA voltage clamp. VCA Active Termination is used to reduce reflection from mismatches and achieving better axial resolution. See VCA Parameters.
- VCA Amplification
- VCA LPF
- VCA LNA Input Clamp
- VCA Active Termination
The analog TGC for RF data collection is determined through a number of parameters. The main TGC curve is specified by TGC:Analog (see System Curves). The maximum depth that the TGC:Analog curve is used to is detemined by TGC:Depth. Depths beyond will use the last calculated value of the curve.
- TGC: Analog
- TGC: Depth
Temporal Shaping of the beam Formed RF data
A user adjustable software digital gain is calculated and applied to the beam formed RF data by the software. The software digital gain has two components, both of which are determined by the user. A depth dependent component which comes from the sliders, and an overall component. This makes the software digital gain dependent on the depth, and hence a TGC in essence.
The gain chosen by the user is Gain:Overall. Its value should be mapped to 0% to 100% in the digital gain range. In order to maintain a uniform look across different frequencies, an offset is added to this overall gain which is determined by Gain: Overall (Digital) Offset. The values of these parameters are on a logarithmic scale and will be the exponent of the actual multiplicative gain. The minimum digital gain (in dB) is determined by Gain:Min Ampl. The size of the range of digital gains possible (in dB) is determined by Gain:Range.
- Gain: Overall
- Gain: Overall (Digital) Offset
- Gain: Range
- Gain: Min Ampl
The TGC curve is adjustable by the user by a set of sliders representing different depths from the console of the ultrasound system. This is accomplished by applying a digital TGC on the beam formed RF data. Slider values from the console are reflected in TGC:Sliders. The effect of the user TGC (sliders) on the overall TGC is determined by TGC:Sensitivity.
- TGC: Sliders
- TGC: Sensitivity
A lateral gain curve is also implemented. This parameter is used for phased array probes only. If the curve is defined in the preset, it gets applied laterally to compensate for the bright middle region. It is applied digitally per scan line. It represents half transducer, applied symmetrically.
- TGC: Lateral
- TGC: Lateral Offset
The system's auto-adjust for the gain can be enabled by the TGC:Auto Enable.
- TGC: Auto Enable
- TGC: Auto Method (debug)
For more info see Gain Engine.